
Sorry but I felt really irritated while reading your comment where you state your own thoughts as facts…
when you read a couple more chapters (maybe the other arcs) you will discover that Tatsuya is by no means a weak/pushover MC. If anything he is maybe overpowered…
and his whole behavior patterns have a very solid (tragic) reason that is also explained in the manga
So if you won't mind please seperate your own evaluations/thoughts from the facts/your observation
thank you

Since you're only commenting on the beginning of the story, maybe you should further your reading, not only to the manga or watching the anime, but the novels as well. After all this is based on a novel and maybe you will understand the characters more. Why the sister have this serious brother complex of her and all other things.
I'm on the other hand is actually interested what would happen if something seriously happens to the sister. Didn't their aunt told him that his sister is important to him since she is like a stopper for him from going berserk or something like that. She was actually made for him and not the other way around. Anyway, i'll just wait until the novels are done before reading again.
Read a few chapters and all I can say is mc is weak as fuck, is a pushover, has sister complex pretty sure if his sister killed him he wouldn't even scold her, can't talk so was forced to join the student council because he didn't want to interrupt his sister while she was making sure he would join. In the end manga is horrible with a weak and pushover mc. Absolutely hate how stupid he is!